1. Field of the Invention
The present invention relates to a sewing machine, and more particularly to speed control of a sewing machine by a wireless controller.
2. Description of the Known Art
As is generally known, a sewing machine has a drive shaft which is rotated by a drive motor to reciprocate a needle carrying an upper thread vertically, and to rotate in synchronism with the needle a loop taker having a lower thread located therein to form stitches. The rotation speed of the drive shaft may be varied by a foot pedal controller or a hand-operated controller which is operative by a variable resistor and connected to the sewing machine by an electric transmission cord or wire. Namely, the rotation speed of the drive shaft is varied by the controller through a speed control circuit which is generally provided in the sewing machine and is operated with a voltage optionally set by the controller to control the rotation speed of the drive motor.
As a result, in case that the sewing machine has the foot-operated controller employed in connection therewith, it becomes necessary to use the electric transmission cord or wire to be connected between the foot-operated controller and the sewing machine having the drive motor provided therein. In this case, the machine user is required to deal with the transmission wire at the beginning and end of machine sewing work, that is, to connect and disconnect the controller wire to and from the sewing machine. The disconnected wire has to be put into order so as not to stand in the way. Moreover, the connected wire will often catch the user's foot by accident. In the case where the conventional hand-operated controller switch is used in connection with the sewing machine, the user is required to use one hand to operate the controller which is connected to the sewing machine by the cord or wire. This requirement is in any event distracting from the handling of the work to be stitched on the sewing machine.
In order to solve the problems inherent in the conventional controller operated sewing machine, a wireless controller of the radio wave type has been proposed for the sewing machine. However, the wireless controller of this type often suffers from radio interference. When the radio wave interference occurs during sewing operation, it may happen that the rotation speed of the sewing machine is out of control to thereby create a danger to the user.